In an electric train car controlling device, the torque of induction motors needs to be suitably controlled such that idling of wheels would not occur to achieve smooth acceleration during power running operation. Patent Document 1, for example, discloses an example structure of an electric train car controlling device for controlling idling during power running operation. The electric train car controlling device drives four induction motors for driving four driving wheel axles with a single inverter.
Specifically, the conventional electric train car controlling device calculates the speed of each axle on the basis of a detection signal detected by a corresponding one of four pulse generators that individually detect the number of revolutions of the four induction motors. Then, the maximum axle speed and the minimum axle speed are selected from the four axle speeds, and a speed deviation ΔV is calculated. Also, the minimum axle speed selected from the four axle speeds is defined as a reference speed V0, reference acceleration a0 is calculated from the reference speed V0, and accelerations α1 to α4 of the axles are calculated from the four axle speeds.
Based on the thus calculated speed deviation ΔV, the reference speed V0, the reference acceleration α0, and the axle accelerations α1 to α4, it is judged whether any wheels of the corresponding axles are in an idling state. For example, in a case where idling occurs at one axle, the idling is detected when the speed deviation ΔV exceeds a set value or when any of the axle accelerations α1 to α4 exceeds the reference acceleration α0 that is an idling detection level. When an idling state is detected, a limiting operation is performed such that a current command value that is supplied from the inverter to the induction motor is temporarily reduced from the original value (target value). Thus, an abnormal vibration phenomenon is prevented from occurring in the electric train car at the time of idling.    [Patent Document 1] Japanese Patent Application Laid-open No. 11-89005 (paragraphs [0002] to [0006], FIG. 19)